As referred to herein, gun barrels or tubes are generally tubular structures through which projectile is fired. Gun barrels may have a smooth bore or be rifled to impart spin and stabilize the projectile being fired. Rifling may take the form of helical grooves formed in the barrel of the gun with groves having sharp or round edges. Polygonal rifling can also be used. Both forms of rifling create helical surface features on the interior of the gun barrel and may be produced by cutting, broaching, hammer-forging, flow-forming, electro-chemical etching or any other surface-shaping or forming technique.
The life of high performance gun barrels is typically limited by their fatigue, wear and erosion characteristics. Thermal impact and structural loading, such as heat and pressure generated by ignition and burning of the propellant, can cause damage to or failure of the gun barrel. The internal surface of gun barrels is also subjected to fatigue, wear and corrosion which elevate with the firing of each projectile. In many cases the need for a reasonable barrel life will limit the overall system performance by precluding modern propelling charge solutions which provide increased performance at the cost of increased barrel fatigue, wear or erosion.
A variety of methods to form protective surface layers on bores of steel gun barrels are known to the art. The nitriding and carburizing processes can be used; typically a very thin surface compound layer and a deeper metallurgically-modified zone are formed. Mechanical inserts made from Stellite™ (a cobalt-based alloy), Inconel™ (a nickel-chromium based alloy) or other high-performance materials are known to be used in gun barrels to subside impact to barrel steel. Steel gun barrels are commercially coated with galvanic chromium to improve the wear resistance of the barrel. Coating of a bore surface of a gun barrel with tantalum is described in U.S. Pat. No. 2,792,657. Explosively welded protective cladding of a gun barrel bore is described in U.S. Pat. No. 3,261,121; the cladding may be of a refractory metal having a melting point higher than chromium.